1. Field of the Invention
The present invention relates to a semiconductor integrated circuits (hereinafter, referred to IC's) suited for computer-aided-design, and more particularly to standard-cell type IC's using poly-cells having improved wiring structure for supplying power.
2. Description of the Related Art
As semi-custom LSI's (Large Scale Integrated circuits) designed in accordance with the customer's specification, the standard-cell type IC's using polycells have been widely used. They are designed by a technique similar to the gate-array type semiconductor integrated circuits (hereinafter, simply referred to the gate-array IC's). In the gate-array process, a plurality of blocks of circuit elements and limited number of wirings are preliminarily formed on a semiconductor chip. An electrical circuit in accordance with the customer's specification is then formed by designing a wiring pattern. The wiring pattern to be designed in the later process include wirings for forming a cell of circuit with the circuit elements in each block, wirings for connecting the cells and wirings for supplying power.
On the other hand, the standard-cell type IC using polycells, the blocks of circuit elements are used in software program for designing an IC. The wirings for forming the polycells of circuit with the circuit elements and for connecting the polycells are also designed by computer-aided-design. All the masks for producing the standard-cell type IC is designed by the computer-aided-design.
In the standard-cell type IC, a plurality of polycells are arranged in lines. The polycells have the same or the substantially same width in a direction perpendicular to the line and arbitrary length in a direction in parallel with the line. The polycells are made of various standardized blocks of circuit elements. The standard-cell type IC's are designed by combining the polycells formed by the standarized blocks. The use of the standardized blocks makes the computer-aided-design of IC easy, resulted in an improvement of design efficiency.
Turning to the design of wirings for power supply, they are designed so as to traverse the polycells and to reach predetermined positions on opposing sides facing the neighbouring polycells. If all the polycells have the same width, the wirings for power supply automatically contact with those in the neighbouring polycells. The cells to be formed in a semiconductor chip, however, may have different dimensions. Cells for specific functions such as RAM (Random Access Memory), ROM (Read-Only Memory), microprocessor, peripheral controller of the microprocessor and PLA (Programable Logic Array) may be included as megacells which have a dimension much larger than the polycells. If the wirings for power supply in the megacells are similarly designed to the polycells, the wirings for power supply differ in position between neighbouring polycell and megacell at their sides facing to each other. Thus, disconnection occurs at contacting sides of those cells having different dimensions.
In the prior art, such disconnection was cured by manual correction of wiring pattern. The manual correction split the production efficiency of the computer-aided-design to raise the production cost and to prolong the production period of term.